* Computer is a concrete noun because it refers to a physical object. You can touch a computer, see it, and interact with it.
* Computer can also function as an abstract noun when it refers to the concept of computing, like in these examples:
* "The advent of the computer revolutionized the world." (Here, "computer" represents the idea of computation itself)
* "He has a brilliant mind for computer science." (Here, "computer" refers to the field of study)
In essence, whether "computer" is abstract or concrete depends on the context of its usage.